# What is the mass of one mole of magnesium nitrate Mg(NO_3)_2?

Jan 2, 2016

Got me! I know that 1 mole of magnesium has a mass of 24.3 g.

#### Explanation:

And I know that 1 mole of nitrogen has a mass of 14.01 g, and that 1 mole of oxygen has a mass of 15.99 g. Do you think that by adding the masses together, appropriately weighted, i.e. $1 \times M g + 2 \times N + 6 \times O$, you would arrive at the formula mass of $M g {\left(N {O}_{3}\right)}_{2}$?

After you do that, you could see if your summation is right. Good luck.

Jan 2, 2016

It is equal to the molecular weight, 147 grams. Use the mole definition.

#### Explanation:

Mole is defined as:

$n = \frac{m}{M r}$

where:

$m$ is the mass in grams.
$M r$ is the molecular weight of the substance.

The molecular weight of a substance is equal to the sum of the molecular weights of the atoms that constitute it. For these atoms:

$M g : 24.3$
$N : 14$
$O : 16$

So the molecular weight:

$M g {\left(N {O}_{3}\right)}_{2} = M g {N}_{2} {O}_{6}$
$M r = 23 + 2 \cdot 14 + 6 \cdot 16$
$M r = 147$

Therefore:

$n = \frac{m}{M r}$

$m = n \cdot M r = 1 \cdot 147 = 147 g r a m s$